This invention relates to a valve operating system for an engine and more particularly to an improved camshaft drive for an internal combustion engine.
Various camshaft driving arrangements have been proposed for internal combustion engines. One of the most popular drive arrangements for driving the camshafts of an engine from the crankshaft includes the use of flexible transmitters such as chains, toothed belts or like. In connection with such flexible transmitters, it is the normal practice to employ a tensioner pulley or sprocket that engages the flexible transmitter and holds it under tension so as to avoid it from becoming displaced from the driving sprocket. It is important that the transmitter does not become disengaged from the driving sprocket because such disengagement can change the effective timing of the valve events in relation to the crankshaft position. Although some small variations can be accommodated in low performance engines, a variation in the timing can not only adversely effect engine performance but can cause damage to the engine if the timing becomes so displaced that the head of the piston contacts the heads of the valves. This problem is much more acute in high performance engines embodying high compression ratios and low combustion chamber clearances.
In addition, the tensioner mechanism normally operates on the return or loose side of the flexible transmitter so as to insure against loss of timing. However, in certain engines and particularly high performance engines, it is not uncommon for the engine to turn briefly in a reverse direction when it is turned off. Under this condition, the normal tensioner mechanism will not insure against loss of timing and the timing drive may jump a cog when such reverse rotation occurs with the aforenoted detrimental effects.
It should be noted that the described problem has been discussed in conjunction with all types of flexible transmitters. The problem is more acute with respect to the use of toothed belts than it is with chains, however, the problem can occur with either type of drive.
It is, therefore, a principal object of this invention to provide an improved valve operating system for an engine wherein it is insured that the valve timing will not jump out of phase regardless of the engine operating condition.
It is a further object of this invention to provide an improved tensioning and related mechanism for the flexible transmitter of a camshaft drive.
It is a further object of this invention to provide a timing control mechanism for a camshaft drive that will insure that the drive does not get out of time during any running condition of the engine, be it normal or abnormal.